Sahih Bukhari, Volume 3, Book47, Number 789

Narrated Asma’ bint Abu Bakr:
My mother came to me during the lifetime of Allah’s Apostle and she was a pagan. I said to Allah’s Apostle (seeking his verdict), “My mother has come to me and she desires to receive a reward from me, shall I keep good relations with her?” The Prophet said, “Yes, keep good relation with her. ”